Broken Bow Lake Management Plan

Broken Bow Lake Management Plan

Background

Broken Bow Lake is located approximately 9 miles north of the town of Broken Bow in McCurtain county, southeast Oklahoma (Figure 1). The lake is operated by the U. S. Army Corps of Engineers (USACE), Tulsa District. Congress authorized the project with the Flood Control Act of July 3, 1958, and the Flood Control Act of October 23, 1967. Construction was completed in October 1968, which impounded approximately 22 miles of the Mountain Fork River. The conservation pool was filled in 1970. The reservoir contains 918,070 acre/feet of water at normal elevation of 599.50 ft. asl with 14,200 surface acres. Elevation at the top of the flood control pool is 627.50 ft. asl. The watershed consists of approximately 754 square miles of forestland within Polk County, Arkansas and LeFlore and McCurtain Counties, Oklahoma. The mountainous terrain is mostly comprised of rocky substrate causing low primary productivity, and slightly acidic pH values for waters in this portion of the state. Table 1 contains a list of physical and chemical characteristics of Broken Bow Lake.

For more information on current and historical reservoir data, visit http://www.swt-wc.usace.army.mil/BROK.lakepage.html.

The dam stands 225 ft. above the streambed, allowing maximum depths to reach 180 ft. beneath the surface of Broken Bow Lake. Well oxygenated, cold water (<45˚F) found in the hypolimnion is released downstream during hydropower production. Bubble plume diffusers lie at the bottom of Broken Bow Lake near the dam. If the hypolimnetic water heats up during the summer months, air is pumped to the diffusers. While bubbles rise towards the surface, they create an upwelling of colder water. This cold water supports a year-round trout fishery in a 12 mile stretch of the river below the dam. The Oklahoma Department of Wildlife Conservation (ODWC) began stocking rainbow trout and brown trout in the Lower Mountain Fork River in 1989 to compensate for cold water releases displacing the native warm water fishery.

Attention – Special regulations apply for the trout stream.

Please visit http://www.wildlifedepartment.com/fishregs.htm to review current license requirements and fishing regulations. Copies of “Regulation Guides” are available at the nearest hunting/fishing license dealer.

Habitat

Fish habitat in Broken Bow Lake is primarily comprised of rock and some flooded timber. Additional habitat includes man-made structures such as rip-rap, brush piles, and boat docks. Steep rocky banks are not suitable for much aquatic vegetation. The ODWC has established and maintained 21 brush piles in Broken Bow Lake. Locations of brush piles are listed in Figure 2 and can be found on the Department’s Interactive Digital Wildlife Atlas at http://www.wildlifedepartment.com/wmas2.htm.

Water Quality

Broken Bow Lake is classified as an oligotrophic reservoir with low primary productivity. Water quality data collected through the Oklahoma Water Resources Board (OWRB) as part of their Beneficial Use Monitoring Program (BUMP) classifies Broken Bow Lake as not supporting to fully supporting the outlined Fish and Wildlife Propagation (FWP) beneficial uses. The complete BUMP report of Broken Bow Lake can be viewed at http://www.owrb.ok.gov/quality/monitoring/bump/pdf_bump/Current/Lakes/brokenbow.pdf. Results presented in this report were obtained quarterly from October 2005 through July 2006. A brief overview of several water quality parameters is included below.

Thermal and Chemical Stratification

Broken Bow Lake was thermally stratified between 29 and 36 ft. during the fall. Dissolved oxygen (D.O.) concentrations below 2.0 ppm accounted for up to 66% of the water column. During the winter, the lake was not thermally stratified and had D.O. values 6.0 ppm. The water column during the spring was weakly stratified with D.O. values remaining above 6.0 ppm. A metalimnetic oxygen deficit occurred throughout the lake during the summer quarter. D.O. values fell below 2.0 ppm between 29 and 36 ft. then increased again. The same phenomena occurred in the past but the cause still remains a mystery. Sites in the upper end of Broken Bow Lake had D.O. values <2.0 ppm for 48 and 62% of the water column during the summer. All D.O. values meet the Oklahoma Water Quality Standards, partially supporting assigned FWP beneficial use.

Productivity

A Trophic State Index (TSI), using Carlson's TSI (chlorophyll-a), was calculated to measure the lake’s productivity. The average TSI was 35, classifying the lake as oligotrophic, indicative of low primary productivity and nutrient levels. This value is similar to that calculated in 2004 (TSI=40), placing the lake within the same trophic category. Chlorophyll-a values remained consistent throughout the year, except one site with mesotrophic values during the winter. Broken Bow Lake is considered fully supporting the FWP beneficial use with lake-wide turbidity values below the criteria of 25 Nephelometric Turbidity Units (NTU). The average secchi disk depth was 115 inches.

Conductivity

Specific conductivity ranged from 25.3 μS/cm to 66.4 μS/cm, indicating extremely low concentrations of ionized salts in Broken Bow Lake. These values are much lower than others typically recorded in Oklahoma lakes. Waters with these values have little buffering capacity and are pH sensitive.

The pH values ranged from 5.73 to 7.56 representing a slightly acidic to neutral system. With 69% of recorded values outside the acceptable range, Broken Bow Lake is not supporting the FWP beneficial use based on pH. Low soil pH in this portion of the state is to blame for slightly acidic conditions.

Fishery

Biologists use a variety of gear types and standardized sampling procedures (SSP) to monitor resident fish populations. Sampling locations in Broken Bow Lake are listed in Figure 3. The major sportfish found in Broken Bow Lake include largemouth bass, spotted bass, smallmouth bass, white bass, hybrid striped bass, white crappie, black crappie, walleye, channel catfish, and flathead catfish. The primary forage species include gizzard and threadfin shad.

The ODWC hatchery system is responsible for species hybridization and mass producing fish for distribution throughout Oklahoma. The fish stocking history for Broken Bow Lake is included in Table 2.

Attention – Special fishing regulations apply for Broken Bow Lake, from the slab at the narrows downstream to the dam: 1) Largemouth and/or Smallmouth bass have a 13 – 16 inch protected slot limit and a creel limit of six combined per day.

Black Bass

Broken Bow Lake offers some of the best bass fishing in the region with three species of black bass; largemouth bass (Micropterus salmoides), spotted bass (Micropterus punctulatus), and smallmouth bass (Micropterus dolomieu). Tournament results for Broken Bow Lake are summarized in Table 3. Ranking of Oklahoma Lakes depends on the number of tournament reports submitted by tournament directors. A black bass creel survey was conducted in 1996 – 1997 at Broken Bow Lake. The survey results are included in Table 4.

Largemouth Bass

The Florida Largemouth Bass (FLMB) subspecies is routinely introduced into Broken Bow Lake because of their potential to reach trophy size. Genetic evaluation is required at least every three years after stocking FLMB. In the past, liver samples were required for 2-loci electrophoresis genetic testing. Advances in genetic research have provided a method of testing using external tissues. Fin clips from 40 age-1 largemouth bass are collected for 3-loci Microsatellite DNA analysis. The new method offers a better approach to determine the success of Florida strain introductions. A 3-year mean percentage of FLMB and/or F1 phenotypes >30% is necessary criteria for stocking requests. Electrophoretic results for Broken Bow Lake largemouth bass are included in Table 5. Based on catch rate criteria, Broken Bow Lake has a low total abundance and a low number of quality sized largemouth bass. Trends show Broken Bow Lakes’s largemouth bass had low relative weights in the past. However, 2009 electrofishing results show the largemouth bass 14 inch group with acceptable relative weights. Over three quarters (78%) of the sample was < 14 inches and 21% was between 13-16 inches in length, with the 13-14 inch group contributing 11% to both. Only 12.2% of the sample was > 16 inches in length. Catch rates and size structure of largemouth bass are included in Table 6 and Figure 4, respectively. Sixty Largemouth bass from Broken Bow Lake were tested for Largemouth Bass Virus (LMBV) in 2003. LMBV was never confirmed at Broken Bow Lake. Otoliths were collected from 20 largemouth bass per inch group during the 2009 electrofishing sample and evaluated to determine a baseline for age and growth (Table 7 and Figure 7). Three different age classes (3-5) had at least some fish < 16 inches long. The slot appears to protect the target length group with relative weights remaining high (13-16 inch Wr = 96). Once largemouth reach 17 inches, their numbers fall off the chart. Largemouth bass must reach 6 years old to see lengths > 16 inches, but growth rates increase after competition is reduced. Broken Bow Lake currently holds the state record largemouth bass that weighed 14 .7 lbs. (28 inches long) caught on 3-14-1999 by William Cross.

Spotted Bass

Spotted bass are abundant (mean catch rates of 48.7 per hour; high total abundance is >30 per hour) in Broken Bow Lake and compete with largemouth bass for the same forage. With “quality” sized ( 14”) spotted bass moderate in abundance, management goals changed. All creel and size limits were removed from spotted bass regulations statewide in 2009. Spotted bass catch rates and size structure of spotted bass are included in Table 8 and Figure 5, respectively. Otoliths were collected from 20 spotted bass per inch group during the 2009 electrofishing sample. These otoliths were evaluated to determine a baseline for age and growth (Table 7 and Figure 7). The age 2 class was 54% of the spotted bass sample with a mean length of 8.6 inches. Mean length at age 3 was 12.6 inches and made up another 29% of the sample. Relative weights are typically good for 8-12” length groups. After spotted bass reach 14 inches at age 4, growth slows to around 1 inch per year. The current lake record spotted bass is 2.4 lbs. at 17 inches long, caught on 12-14-2008 by Bryce Archey.

Smallmouth Bass

A genetic survey across the natural range of smallmouth bass conducted in the 1990s demonstrated that the native populations in eastern Oklahoma represent the two most divergent lineages of the species; referred to as the Ouachita and Neosho smallmouth bass (Stark and Echelle 1998). The ODWC previously stocked “Tennessee lake strain” smallmouth bass into Broken Bow Lake in 1993. Based on an allozyme survey by Stark el al. (1995), the ODWC discontinued stockings over concerns of losing genetic diversity. The genome of the Broken Bow Lake population is about 40% non-native. A small amount (3%) of non-native material has made its way into the Mountain Fork River. The upper end of Broken Bow Lake acts as a partial barrier to dispersal. However, increased introgression of the “lake strain” into the tributaries is likely to occur. The quality of the smallmouth bass fishery may be dependent on the growth and survival of the “lake-strain” or F1 hybrid (Boxrucker et al. 2004). Smallmouth bass total abundance is currently below recommended levels. Zero quality sized smallmouth bass were collected during the spring electrofishing survey. Relative weights are acceptable for the 10-12 inch group. Age and growth results from the 2004 study are included in Table 9. Otoliths were also collected from 15 smallmouth bass during the 2009 electrofishing sample and evaluated for age and growth (Table 7 and Figure 7). In 2009, mean length at ages 2-3 resembled spotted bass results. Age/growth data from the 2004 survey shows lengths of individual ages from Broken Bow Lake and the Mountain Fork River are statistically different. By age 4, “Lake” smallmouth bass mean lengths were 5 inches longer than the “River” smallmouth bass. Catch rates and size structure of smallmouth bass are included in Table 10 and Figure 6, respectively. The current lake record smallmouth bass weighs 5.7 lbs. (22 inches long) caught on 2-9-2008 by Chuck Tillman. Broken Bow produced two former state record smallmouth bass that weighed 5.1 lbs. and 5.6 lbs., in 1980 and 1983, respectively.

Temperate Bass

White Bass

White Bass (Morone chrysops) are very important to the Broken Bow Lake recreational fishery. There is a moderate total abundance and a high abundance of quality sized ( 12”) white bass in Broken Bow Lake. White bass create a popular spring fishery in the narrows of Broken Bow Lake and its tributaries during their spawning run. Relative weights are good at 103; acceptable values are 90. Catch rates and size structure of the Broken Bow Lake white bass fishery are included in Table 11 and Figure 8, respectively.

Hybrid Striped Bass

The ODWC hatchery system has collected white bass from the narrows as part of a reciprocal hybrid striped bass (F1: female Morone chrysops x male M. saxatilis) experimental stock in some Oklahoma lakes. Hybrid striped bass (likely F1: male Morone chrysops x female M. saxatilis) were recently found in Broken Bow Lake in moderate abundance with a mean catch rate of 4.7 per 24 hours. The ODWC is not responsible for their presence in Broken Bow Lake. Circumstances surrounding the introduction of this species remain unknown. Hybrid striped bass reach large sizes, creating exciting fishing opportunities. Recent SSP results show a high percentage of the catch in the 12-14 inch length groups. However, 2 individuals represented the 23 inch group (~ 6 lbs.) suggesting separate age classes. A complete overview of the Broken Bow Lake hybrid striped bass fishery is included in Figure 9.